A flow of liquid, such as water or oil, can be established in a piping network, by means of oscillating positive-displacement pumps which are commonly reciprocating pumps or diaphragm pumps. Due to the dynamics of producing pressure e.g. by a crank-drive reciprocating pump, some periodic fluctuation or pulsation is imposed upon the displaced volume or liquid flow, depending on the type of motion of the drive. Such pulsations of pressure and flow are undesirable not only for the user who as a rule requires a very steady flow, but also because of the risk that the service life of various components of the piping network, e.g. of valves and instruments, may suffer severe detrimental effect. Since liquids such as water are relatively incompressible, there may occur in the piping network vibrations or pulsations the amplitudes of which may, unless dampened, reach 12 to 15 (1 b-1 bar=10.sup.5 N/m.sup.2) with a pressure level of about 200 (1 b=1 bar=10.sup.5 N/m.sup.2 at the delivery side. The frequencies of such vibrations or pulsations depend on the speed or working frequency of the positive-displacement pump on the one hand and on the structure of the piping network on the other hand. Heretofore, so-called air chambers or antifluctuators have been used for dampening liquid pulsations. Such devices required considerable maintenance. More recently, hydro-pneumatic antishock devices have been rather widely installed in piping networks for attenuating pulsations. These devices are also termed absorption dampeners and require much less maintenance work.
U.S. Pat. No. 3,628,573 to Loliger et al, discloses a hydro-pneumatic pulsation dampener comprising a resilient diaphragm within a housing composed of two shells. A chamber containing a volume of gas is separated by means of this diaphragm from another chamber through which the liquid passes. Thus any such hydro-pneumatic vibration dampener will contain, within a receptacle, a gas volume separated from the liquid by a movable wall, in particular by a diaphragm or a piston. Attenuation is due to the hydraulic coupling between the displacer's motion and the liquid in the piping network being presented to the gas cushion mentioned, in which the compressibility of the gas is exploited for dampening.
Absorption dampeners or hydro-pneumatic vibration dampeners of this type are arranged in a by-pass for reasons of strength and ease of maintenance. In view of the dependence of the extent of pulsation on the pump delivery pressure, it would be possible to employ other absorption dampeners having different characteristics for varying pressures or generally high requirements to the suppression of pulsations. Alternatively, the number of absorption dampeners might be increased. However, the expenditures involved would be out of proportion to the residual pulsation remaining.
Aside from absorption dampeners, reflection pulsation dampeners have come into use, designed as resonators based on dynamic action principles. The effect of such reflection dampeners is due to a partial reflection of an oncoming sound wave at the location of a ramification or of a brusque change of cross section in a pipeline, as the condition for continuity of acoustic pressure and of sound propagation must be satisfied. Such reflection dampeners are devoid of movable mass-carrying components. A particular embodiment is described in U.S. Pat. No. 3,731,709; to Glover, which features, within a housing, deflection means comprising two spaced manifold plates in which there are nozzle bores for passing the liquid. The liquid is made to move in an orbital-flow or spin pattern by these deflection means.
While the conventional reflection dampeners require practically no maintenance, they are disadvantageous in that for attaining small residual pulsation, they must have large volumes or even several chambers. Moreover, the overall length will increase, the lower the frequency of the vibration wave in the piping network is. The resulting large space requirement and the considerable cost involved have brought about some restrictions on the use of reflection dampeners despite their satisfactory attenuation owing to the arrangement in the main flow path.